I don't think the Necron codex allows for the more "horde" feel that people want from the undead, its a start though
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As well as the aforementioned Typhus and Necrons, Dark Eldar could do a decent Undead-feeling list, with hordes of Wracks acting as zombies, grotesques/talos/cronos being weird flesh-constructs, haemonculi as Liches and such. Ally in some Farseers and Guardians for Necromancers and cultists.
You absolutely can still do that.
Warriors and Immortals are 13 and 17 points apiece, respectively, and you can back them up with res. orbs or Ghost Arks (for the warriors) to enhance their reanimation capabilities.
Warriors are the best bet because they're cheaper and can go in blobs of 20, and you can use a couple strategically-placed Ghost Arks to support a few squads - and the Ghost Ark's repair ability is something completely different from the resurrection orb's enhancement of reanimation protocols, so the abilities stack to make the units even more resilient.
Combined with all gauss weaponry auto-glancing vehicles on a 6, there's no reason that strategy isn't viable if it's something you really want to go for.